Electronic sorting device having improved automatic calibration means



Nov. 24, 1970 H, BUTTERWORTH ET AL 3,543,027

ELECTRONIC SORTING DEVICE HAVING IMPROVED AUTOMATIC CALIBRATION MEANS Filed Feb. 29, 1968 POTENTIOMETER VELOCITY MGOVERNOR 7V COMPARATOR l 2 X-RAY TUBE COLE AGE

United States Patent 01 fice 3,543,027 Patented Nov. 24, 1970 3,543,027 ELECTRONIC SORTING DEVICE HAVING IM- PROVED AUTOMATIC CALIBRATION MEANS Harold Millman Butterworth, Henry Albert Nickless, and Louis Maule-Cole, Sussex, England, assignors, by mesne assignments, to US. Philips Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 20, 1968, Ser. No. 706,839 Claims priority, application Great Britain, Feb. 20, 1967, 7,884/ 67 Int. Cl. G01t 1/16 U.S. Cl. 250-83 11 Claims ABSTRACT OF THE DISCLOSURE Apparatus for automatically calibrating the gain potentiometer of an electronic sorting device includes an electromagnetic clutch for selectively coupling the potentiometer to a spring biased handle. The handle is coupled to the potentiometer so that movement of the handle to an end position moves the pot arm to an extreme position also. A comparaor energizes the clutch as the handle is urged to its rest position by the spring. The comparator deenergizes the clutch at the correct calibration point, disengaging the potentiometer from the handle, which moves on until it reaches its rest position.

The present invention concerns control devices, and is particularly but not solely concerned with normalising the outputs of a number of photomultipliers.

One example of the many possible applications of such a device occurs in apparatus for sorting wanted pieces of material from unwanted rubbish, such as potatoes from stones and clods. In such apparatus the mixture of potatoes and stones are moved past a number of X-ray beams falling on a similar number of detectors in the form of photomultipliers. The output of each photomultiplier when its associated beam is obscured by an object depends on the nature of the object. In dependence upon the output of a photomultiplier a finger is moved to divert the object passing through the X-ray beam into one of two paths, one path for potatoes and the other for rubbish. In one example of a potato sorting apparatus there may be eight photomultipliers associated with eight finger mechanisms. It is of course essential that each photomultiplier operates its associated finger mechanism at the same output level in response to a standard input. Thus, ideally each photomultiplier should have the same gain as the other photomultipliers. This is difficult to obtain.

Accordingly each photomultiplier is usually provided with a potentiometer for controlling its gain. It is then possible to calibrate each photomultiplier individually by introducing a suitable filter between each photomultiplier and the X-ray source, said filter having an impedance value with regard to X-rays representing a mean value which acts as the dividing line between, for example, potatoes and rubbish.

This process is, however, time consuming and also requires a certain degree of skill which would probably not be present in a farm hand looking after a potato sorting machine.

Accordingly, an object of the present invention is to provide apparatus which can, in one operation, set the output of a number of electronic devices at a predetermined level, and in particular can set the gain of a number of photomultipliers so that the photomultipliers provide similar outputs in response to a standard input.

According to the present invention, there is provided an apparatus for adjusting the output of an electronic device supplying an output signal which varies in response to a physical quantity. The apparatus comprises a potentiometer controlling the output of said device, means for producing a standard input to the device and for altering the value of the potentiometer during such input, means for comparing the output of the potentiometer with a standard signal corresponding to the output required from the device in response to the standard input, and means for stopping the potentiometer at the value a which its output is the same as the standard signal.

One embodiment of the invention will now be particularly described hereinafter, by way of example, and with reference to the accompanying drawing which is a diagrammatic view of apparatus constructed in accordance with the present invention for setting the gain of a photomultiplier to a predetermined level.

The device shown in the drawing has a photomultiplier 1 arranged to receive a beam of radiation from an X-ray tube 2. The device forms part of a potato separator in which potatoes, stones and clods are moved through the X-ray beam and the output of the detector is used to actuate a finger mechanism in accordance with the nature of the object passing through the beam, thus separating the potatoes from the clods and stones. Although in the accompanying drawing only one photomultiplier is shown, it is to be assumed that there are in fact eight photomultipliers. It is accordingly necessary to ensure that all of the photomultipliers supply the same output in response to identical inputs. Accordingly, photomultiplier 1 has associated with it a potentiometer 3 controlling its gain, and each of the other photomultipliers, which are not shown, will have similar otentiometers. The potentiometer 3 is coupled to a handle 4 by means of peg and pin plates 5. The elements are arranged so that when the handle 4 is pulled against the spring 6 to its extreme position, as shown in the drawing, the potentiometer 3 is returned to its minimum gain position. The handle 4 has a projection 7 which engages one end of a slot 8 just before the handle 4 reaches its final position. The final movement of the handle 4 thus moves a filter plate 9 of known density between the photomultiplier 1 and X-ray tube 2, and at the same time closes a pair of contacts 10 which connect an electromagnetic clutch 11 to the output of a comparator 12. The output of the potentiometer is supplied to the comparator 12 as well as to the remainder of the sorting mechanism, which is not shown. The clutch 11 transmits drive from the handle 4 to the potentiometer through a gear train 13.

The filter plate 9 is arranged to represent a critical value of impedance to the X-ray beam so that the photomultiplier 1 has a standard input when the plate 9 is in position, the plate 9 having the same etfect as if a small stone were in the path of the X-ray beam.

The comparator 12 is so arranged that an output is obtained when the output of the photomultiplier 1 is below the level required by the presence of the filter plate 9 in the path of the X-ray beam. Thus, under these conditions the photomultiplier gain is very low and the output of the comparator 12 energizes the clutch 11. Thus when the spring 6 returns the handle 4 to its original position, the potentiometer 3 is driven via gear train 13. The gain of the photomultiplier 1 increases until the output reaches a level such that the comparator output reduces to zero, thus deenergizing the electromagnetic clutch and leaving the potentiometer 3 in the correct position. Just before the handle reaches its initial position the projection 7 engages with the other end of the slot 8 and removes the filter plate 9 from the path of the beam and opens the contacts 10.

The return movement of the handle is kept at a constant speed by a velocity governor 14.

It should be realised however, that the present invention is not solely concerned with photomultipliers. Instead, the apparatus might be used to control the outputs of a number of photoelectric cells, in which case the plate 9 could be replaced by a suitable light filter.

It is also conceivable that the apparatus might be used in conjunction with heat dependent resistors. In this case the apparatus would compensate for variations in the temperature coefficients of a number of such resistors. A standard heat source would be used instead of a filter.

Several modifications of the apparatus described hereinbefore are also possible. For example, it is not necessary for the potentiometer to be driven from its position of minimum gain by the movement of the handle. Any other suitable means, such as an electric motor, for driving the potentiometer while the filter plate is in position could be used.

The required standard output can be varied by having a number of filter plates 9, which can be selected in any suitable manner.

What We claim is:

1. Apparatus for adjusting the output of an electronic device that produces an output signal which varies in response to a physical quantity comprising, a potentiometer coupled to said device for controlling the output signal thereof, means for moving said potentiometer to one extreme position to calibrate said apparatus, means for supplying a standard input to the device, means for driving the potentiometer towards the other extreme position while said standard input is supplied to said electronic device, means for comparing the output of said device with a standard signal corresponding to the output required from the device in response to the standard input, and means for stopping the potentiometer at a given value at which the device output is the same as the standard signal.

2. Apparatus as claimed in claim 1 in which the device includes a photomultiplier, the gain of which is controlled by the potentiometer.

3. Apparatus as claimed in claim 2 in which the means for producing a standard input comprises a filter which can be positioned between the photomultiplier and a source of X-rays.

4. Apparatus as claimed in claim 3 further comprising means for mechanically coupling the filter to the potentiometer so that when the filter is moved into position between the photomultiplier and the X-ray source the potentiometer is moved to an extreme position of either maximum or minimum gain.

5. Apparatus as claimed in claim 4 wherein said comparing means comprises a comparator, means for coupling the output of the potentiometer to the comparator which produces an output when the output of the photomultiplier is not at the required level, an electromagnetic clutch for selectively coupling the potentiometer with said driving means, and means coupling the output of the comparator energising to the electromagnetic clutch to energize same to transmit drive to the potentiometer from the driving means.

6. Apparatus as claimed in claim 5 further comprising a movable handle member spring biased to one extreme position, the electromagnetic clutch coupling the potentiometer to a gear train driven by the movement of said handle member as the latter moves from a first extreme position to a second extreme position under the influence of said spring biasing.

7. Apparatus as claimed in claim 6 further comprising means mechanically coupling the handle member with the filter so that when the handle member is moved from the second extreme position to the first extreme position it moves the filter into is operative position.

8. Apparatus as claimed in claim 7 further comprising a speed governor for controlling the movement of the handle member from its first to its second extreme position while under the influence of the spring biasing.

9. Apparatus as claimed in claim 1 further comprising a radiation source spaced from said device, said standard input supplying means comprising a filter movable into position between said radiation source and said electronic device, and means for mechanically coupling the filter to the arm of the potentiometer so that movement of the filter into position between said source and said device moves the potentiometer arm to an end position.

10. Apparatus as claimed in claim 1 further comprising a radiation source spaced from said device, said standard input supplying means comprising a filter movable into position between said radiation source and said electronic device, and wherein said potentiometer stopping means comprises an electromagnetic clutch arranged to selectively couple the potentiometer with said driving means and energized by the output of said comparing means.

11. Apparatus as claimed in claim 10 wherein said driving means includes a handle member movable between first and second positions and selectively coupled to said potentiometer by means of said clutch, and means for urging said handle member towards said first position.

References Cited .UNITED STATES PATENTS 2,884,530 4/1959 Foster 250 -83 3,291,981 12/ 1966 Stock 2508 3 3,348,046 10/ 1967 Lloyd 250-83 3,390,769 7/1968 Tatham et a1. 250-833 ARCHIE R. BORCHELT, Primary Examiner US. Cl. X.R. 25083.3 

